This invention relates to an enrichment method of carbon 13 by use of laser rays and particularly to an enrichment method of carbon 13 by means of laser isotope separation by way of infrared multiple-photon decomposition.
Natural carbon comprises isotopes of mass-numbers 12 and 13, ratios of which are 98.9% and 1.1%, respectively. Conventional enrichment methods of carbon 13 are based on low temperature distillation of CO, but these methods have such disadvantages that a large amount of poisonous gas should be used, large scale apparatus should be used and manufacturing cost is high. Therefore, it is very significant if carbon 13 is separated safely and cheaply by use of laser irradiation.
We will explain prior art enrichment methods of carbon 13 by the laser irradiation.
Working substance such as CF.sub.3 X (wherein X is Cl, Br or I), or CF.sub.2 HCl is irradiated with laser rays emitted from a CO.sub.2 laser. In the infrared multiple photon decomposition of CF.sub.3 X, the final product is C.sub.2 F.sub.6. In the infrared multiple photon decomposition of CF.sub.2 HCl, the final product is C.sub.2 F.sub.4. The final products are enriched with Carbon 13.
In this method, so long as practically meaningfully high yield is intended, the ratio of carbon 13 after the enrichment is only 80% and does not reach to the ratio obtained in the conventional enrichment methods by way of the low temperature distillation of CO. In the method described in Japanese patent application public disclosue No. 60(1985)-132629, C.sub.2 F.sub.6 is irradiated in presence of Br.sub.2 with pulsed laser rays emitted from a CO.sub.2 laser with adequate wavenumber and fluence. As a result of the photo-dissociation and the subsequent reaction, CF.sub.3 Br is produced which is enriched with carbon 13 to a ratio of 20% to 30%. Next, the product CF.sub.3 Br is separated and once more irradiated with pulsed laser rays emitted from a CO.sub.2 laser under particular conditions to induce an infrared multiple photon decomposition. The product of the second infrared multiple photon decomposition is C.sub.2 F.sub.6, in which the ratio of carbon 13 is increased to 90%.